CN112769492A

CN112769492A - Method and device for monitoring modulation depth of direct current bias jitter signal and optical transmitter

Info

Publication number: CN112769492A
Application number: CN201910998746.9A
Authority: CN
Inventors: 李静楠; 樊洋洋; 陶振宁
Original assignee: Fujitsu Ltd
Current assignee: Fujitsu Ltd
Priority date: 2019-10-21
Filing date: 2019-10-21
Publication date: 2021-05-07
Also published as: US11057106B2; US20210119699A1; JP2021067933A

Abstract

The embodiment of the application provides a method and a device for monitoring the modulation depth of a jitter signal and an optical transmitter, wherein the device comprises: a detector which detects an optical signal output from the mach-zehnder modulator to obtain an electrical signal, wherein a dither signal of a predetermined frequency is superimposed on a dc bias voltage applied to the mach-zehnder modulator; a double-frequency dither signal synchronous detection module, configured to perform synchronous detection on the electrical signal output by the detector and a double-frequency dither signal with a frequency 2 times that of the predetermined frequency to obtain an amplitude of a signal component included in the electrical signal output by the detector and having a frequency identical to that of the double-frequency dither signal; and a signal processor which calculates a modulation depth of the dither signal superimposed on the dc bias voltage according to an amplitude of the double frequency dither signal.

Description

Method and device for monitoring modulation depth of direct current bias jitter signal and optical transmitter

Technical Field

The present application relates to the field of optical communications technology.

Background

In coherent optical communication, a Mach-Zehnder (M-Z) modulator serves as an important device in an optical transmitter to convert an electrical signal into an optical signal.

The mach-zehnder modulator is inputted with a predetermined dc bias voltage and can operate at a corresponding operating point. If the dc bias voltage input to the mach-zehnder modulator is shifted, the communication quality is degraded.

In order to monitor the dc bias state of the mach-zehnder modulator, researchers have proposed various methods, such as loading a low-frequency dither signal directly on the dc bias voltage, or monitoring the dc bias voltage of the mach-zehnder modulator by loading a low-frequency dither signal on a radio-frequency signal through a driving amplifier.

When applying a dither signal, the modulation depth is controlled within a reasonable range. Modulation depth and amplitude alpha of loaded dither signal and half-wave voltage V of Mach-Zehnder modulator_πIs dependent on the ratio of (a) to (b), e.g. when the optical modulator is a differential mach-zehnder modulator, the modulation depth of the dither signal is defined as

When the optical modulator is a single-ended Mach-Zehnder modulator, the modulation depth of the dither signal is defined as

When the modulation depth of the jitter signal is small, the corresponding monitoring quantity can be submerged in noise, and the bias state of the modulator cannot be effectively monitored; when the modulation depth of the jitter signal is large, the jitter signal may interfere with the driving signal as a kind of noise, thereby causing an additional bit error cost and deteriorating the communication quality.

The traditional Mach-Zehnder modulator usually adopts lithium niobate, the modulator prepared by lithium niobate materials has a linear volt-phase relation, the half-wave voltage of the modulator is not dependent on a direct current bias point, but is determined by the self characteristics of the modulator and is nonadjustable, and therefore the modulation depth of a jitter signal can be controlled only by adjusting the amplitude of the jitter signal. Usually, after the working performance of the modulator and the cost of the jitter signal are considered in a compromise, the amplitude of the jitter signal is fixed at a reasonable value, and therefore, the modulation depth is basically considered as a fixed value.

It should be noted that the above background description is only for the convenience of clear and complete description of the technical solutions of the present application and for the understanding of those skilled in the art. Such solutions are not considered to be known to the person skilled in the art merely because they have been set forth in the background section of the present application.

Disclosure of Invention

The inventors of the present application found that: in recent years, mach-zehnder modulators based on various different materials, such as indium phosphide modulators, silicon-based modulators, and the like, have been increasingly developed, the voltage phase relationship of these modulators is no longer linear, and the half-wave voltage thereof depends on the dc bias point, so that the modulation depth of the dither signal is related not only to the amplitude of the dither signal but also to the nonlinearity of the voltage phase relationship, the magnitude of the dc bias voltage, and other factors, and different modulation depths of the dither signal may cause different degrees of dither signal costs. Therefore, the modulation depth of the dither signal needs to be accurately monitored so as to adjust the amplitude of the dither signal more reasonably, thereby controlling the modulation depth within a reasonable range.

The embodiment of the application provides a method, a device and electronic equipment for monitoring the modulation depth of a jitter signal, wherein the device detects an optical signal output by a Mach-Zehnder (M-Z) modulator to obtain an electric signal, calculates the modulation depth of the jitter signal according to the amplitude of a double-frequency jitter signal contained in the electric signal, and can accurately monitor the modulation depth of the jitter signal.

According to a first aspect of embodiments of the present application, there is provided an apparatus for monitoring a modulation depth of a jitter signal, including: a detector which detects an optical signal output from the mach-zehnder modulator to obtain an electrical signal, wherein a dither signal of a predetermined frequency is superimposed on a dc bias voltage applied to the mach-zehnder modulator; a double-frequency dither signal synchronous detection module, configured to perform synchronous detection on the electrical signal output by the detector and a double-frequency dither signal with a frequency 2 times that of the predetermined frequency to obtain an amplitude of a signal component included in the electrical signal output by the detector and having a frequency identical to that of the double-frequency dither signal; and a signal processor which calculates a modulation depth of the dither signal superimposed on the dc bias voltage according to an amplitude of the double frequency dither signal.

According to a second aspect of the present embodiment, there is provided a method of monitoring a modulation depth of a dither signal, comprising: detecting an optical signal output by a Mach-Zehnder modulator to obtain an electrical signal, wherein a direct current bias voltage applied to the Mach-Zehnder modulator is superposed with a jitter signal with a preset frequency; synchronously detecting the electric signal and a frequency-doubled jittering signal with the frequency 2 times of the preset frequency to obtain the amplitude of a signal component contained in the electric signal and having the same frequency as the frequency of the frequency-doubled jittering signal; and calculating the modulation depth of the dither signal superposed on the DC bias voltage according to the amplitude of the frequency doubling dither signal.

According to a third aspect of the present embodiment, there is provided an optical transmitter comprising the apparatus of the first aspect of the embodiments.

The beneficial effect of this application lies in: the optical signal output by the Mach-Zehnder (M-Z) modulator is detected to obtain an electrical signal, the modulation depth of the jitter signal is calculated according to the amplitude of the double-frequency jitter signal contained in the electrical signal, and the modulation depth of the jitter signal can be accurately monitored.

Specific embodiments of the present invention are disclosed in detail with reference to the following description and drawings, indicating the manner in which the principles of the invention may be employed. It should be understood that the embodiments of the invention are not so limited in scope. The embodiments of the invention include many variations, modifications and equivalents within the spirit and scope of the appended claims.

Features that are described and/or illustrated with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments, in combination with or instead of the features of the other embodiments.

It should be emphasized that the term "comprises/comprising" when used herein, is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps or components.

Drawings

The accompanying drawings, which are included to provide a further understanding of the embodiments of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. It is obvious that the drawings in the following description are only some embodiments of the invention, and that for a person skilled in the art, other drawings can be derived from them without inventive effort. In the drawings:

fig. 1 is a schematic diagram of an apparatus for monitoring a modulation depth of a dither signal according to a first aspect of an embodiment of the present application;

FIG. 2 is a schematic diagram of a single Mach-Zehnder (M-Z) modulator of a first aspect of an embodiment of the present application;

FIG. 3 is a schematic diagram of an IQ Mach-Zehnder (M-Z) modulator of a first aspect of an embodiment of the present application;

FIG. 4 is a schematic diagram of a method of calculating a multiplicative component;

FIG. 5 is a schematic diagram of a method of calculating signal components;

FIG. 6 is a schematic diagram of a method of setting an initial modulation depth;

FIG. 7 is a schematic diagram of a method of monitoring the modulation depth of a jittered signal of the second aspect of an embodiment of the present application;

fig. 8 is a schematic block diagram of a system configuration of an optical transmitter of the third aspect of the embodiment of the present application.

Detailed Description

The foregoing and other features of the invention will become apparent from the following description taken in conjunction with the accompanying drawings. In the description and drawings, particular embodiments of the invention have been disclosed in detail as being indicative of some of the embodiments in which the principles of the invention may be employed, it being understood that the invention is not limited to the embodiments described, but, on the contrary, is intended to cover all modifications, variations, and equivalents falling within the scope of the appended claims.

In the embodiments of the present application, the terms "first", "second", and the like are used for distinguishing different elements by reference, but do not denote a spatial arrangement, a temporal order, or the like of the elements, and the elements should not be limited by the terms. The term "and/or" includes any and all combinations of one or more of the associated listed terms. The terms "comprising," "including," "having," and the like, refer to the presence of stated features, elements, components, and do not preclude the presence or addition of one or more other features, elements, components, and elements.

In the embodiments of the present application, the singular forms "a", "an", and the like include the plural forms and are to be construed broadly as "a" or "an" and not limited to the meaning of "a" or "an"; furthermore, the term "the" should be understood to include both the singular and the plural, unless the context clearly dictates otherwise. Further, the term "according to" should be understood as "at least partially according to … …," and the term "based on" should be understood as "based at least partially on … …," unless the context clearly dictates otherwise.

First aspect of the embodiments

A first aspect of embodiments of the present application provides an apparatus for monitoring a modulation depth of a dither signal.

Fig. 1 is a schematic diagram of an apparatus for monitoring a modulation depth of a dither signal according to a first aspect of an embodiment of the present application, fig. 2 is a schematic diagram of a single mach-zehnder (M-Z) modulator according to the first aspect of an embodiment of the present application, and fig. 3 is a schematic diagram of an IQ mach-zehnder (M-Z) modulator according to the first aspect of an embodiment of the present application.

As shown in fig. 1, the device 2 for monitoring the modulation depth of the dither signal monitors in accordance with the optical signal output from the optical modulation unit 1.

As shown in fig. 1, the light modulation unit 1 may include: a mach-zehnder (M-Z) modulator (optical modulator) 11, a laser 12, and a drive amplifier 13.

In at least one embodiment, the Mach-Zehnder (M-Z) modulator 11 may be a single Mach-Zehnder (M-Z) modulator as shown in FIG. 2, an IQ Mach-Zehnder (M-Z) modulator as shown in FIG. 3, or other forms of Mach-Zehnder (M-Z) modulators.

Wherein, V of FIG. 2_RFRepresenting an input drive signal, V_DCRepresents a dc bias voltage; v of FIG. 3_{RF_I}Representing the input drive signal, V, of an in-phase (I) modulator_{DC_I}Representing the DC bias voltage, V, of an in-phase (I) modulator_{RF_Q}Representing the input drive signal, V, of a quadrature (Q) modulator_{DC_Q}Indicating the DC bias voltage, V, of a quadrature (Q) modulator_{DC_P}Indicating the dc bias voltage of the quadrature phase adjustment unit.

In at least one embodiment, the mach-zehnder modulator 11 may be applied with a direct current bias voltage, whereby the mach-zehnder modulator 11 operates at an operating point corresponding to the direct current bias voltage. The laser 12 provides an optical carrier to the mach-zehnder (M-Z) modulator 11, and the drive amplifier 13 amplifies the drive signal and inputs the amplified drive signal to the mach-zehnder (M-Z) modulator 11.

In at least one embodiment, the apparatus 2 for monitoring the modulation depth of the dither signal has: a detector 21, a double frequency dither signal synchronization detection module 22, and a signal processor (signal generator) 23.

As shown in FIG. 1, the detector 21 detects an optical signal output from the Mach-Zehnder (M-Z) modulator 11 to obtain an electrical signal in which a DC bias voltage applied to the Mach-Zehnder modulator 11 is superimposed with a predetermined frequency f_dThe jitter signal of (1).

As shown in FIG. 1, the double-frequency-jitter signal synchronous detection module 22 synchronizes the electrical signal output from the detector 21 with a predetermined frequency f _d2 times (i.e. frequency 2 f)_d) The double frequency jitter signal is synchronously detected to obtain an electric signal packet output by the detector 21Amplitude Coef (2 f) of dither signal with double frequency_d)。

As shown in FIG. 1, the signal processor 23 synchronizes the amplitude Coef (2 f) of the signal component obtained by the detection module 22 according to the frequency-doubled wobble signal and having the same frequency as the frequency of the frequency-doubled wobble signal_d) Calculating the modulation depth of the dither signal superimposed on the DC bias voltage

According to the first aspect of the embodiment of the present application, the apparatus 2 for monitoring the modulation depth of the dither signal detects the optical signal output by the mach-zehnder (M-Z) modulator 11 to obtain the electrical signal, and calculates the modulation depth of the dither signal according to the amplitude of the dither signal with twice frequency included in the electrical signal, thereby accurately monitoring the modulation depth of the dither signal, conveniently and reasonably adjusting the amplitude of the dither signal, and controlling the modulation depth within a reasonable range.

In at least one embodiment, as shown in fig. 1, the apparatus 2 for monitoring the modulation depth of the jitter signal may further have: the original frequency jittering signal synchronization detection module 24.

The original frequency jitter signal synchronous detection module 24 combines the electrical signal output by the detector 21 with a frequency of a predetermined frequency f_dThe original frequency jitter signal is synchronously detected to obtain the amplitude Coef (f) of the signal component which is contained in the electric signal output by the detector 21 and has the same frequency as the original frequency jitter signal_d)。

Wherein, the signal processor 23 synchronizes the amplitude Coef (2 f) of the signal component with the frequency of the double-frequency jittering signal obtained by the detection module 22 according to the double-frequency jittering signal_d) And the amplitude Coef (f) of the signal component with the same frequency as the original frequency jitter signal obtained by the original frequency jitter signal synchronous detection module 24_d) Calculating the modulation depth of the dither signal superimposed on the DC bias voltage

Thus, in the absence ofIn the case of the original frequency jitter signal synchronization detection module 24, the signal processor 23 can be based on Coef (2 f)_d) Calculating modulation depth of dither signal

With the original frequency jittered signal synchronization detection module 24, the signal processor 23 can be based on Coef (2 f)_d) And Coef (f)_d) Calculating modulation depth of dither signal

In the first aspect of the embodiment of the present application, the operation principle of the apparatus 2 for monitoring the modulation depth of the jitter signal will be described by taking, as an example, the case where the mach-zehnder (M-Z) modulator 11 is a differential IQ mach-zehnder (M-Z) modulator. The description is also applicable to the case where the mach-zehnder (M-Z) modulator 11 is of another type.

In at least one embodiment, when the I-modulator of the differential IQ mach-zehnder (M-Z) modulator 11 is biased near the extinction point (i.e., the bias voltage is offset from the bias voltage corresponding to the extinction point), the Q-modulator is biased at the extinction point, and the quadrature phase adjustment unit is biased at the quadrature point, the optical field at the output of the differential IQ mach-zehnder (M-Z) modulator 11 can be expressed by the following equation (1):

wherein the content of the first and second substances,

and

for the optical phase change caused by the loaded driving signals on the IQ two paths,

for I modulator DC offset causeThe amount of phase shift of (a) is,

is a dither signal V_dInduced optical phase change, P₀Outputting optical power for the laser 12. Dither signal V_dIs a low frequency cosine signal and can be written as the following equation (2):

V_d＝αcos(ω_dt) (2)

where α is the dither signal V_dAmplitude of (a), ω_dIs the angular frequency of the dither signal, where ω_d＝2πf_d. Since the dither signal is a small signal, the differential type IQ mach-zehnder (M-Z) modulator 11 may still be considered to have a local linear characteristic at the small signal, and the local slope may be written as

And the local slope may vary with the bias point, i.e. at different bias points, due to

Are different to cause

Different. Therefore, the optical phase change caused by the dither signal can be expressed as the following equation (3):

an optical signal output from the differential IQ Mach-Zehnder (M-Z) modulator 11 is detected by a detector 21, and an electric signal P is obtained_PDCan be written as:

due to the small signal approximation, i.e.,

and

the electric signal P_PDCan be represented by the following formula (4):

the original frequency jitter signal synchronous detection module 24 detects the electrical signal P_PDAnd a frequency of f_dThe original frequency jitter signal cos (2 pi f)_dt) performing synchronous detection, wherein the result of the synchronous detection can be expressed as the following formula (5):

the double frequency dithering signal synchronous detection module 22 will detect the electric signal P_PDAnd a frequency of 2f_dIs the double frequency jitter signal cos (4 pi f)_dt) performing synchronous detection, wherein the result of the synchronous detection can be expressed as the following formula (6):

in the formulae (5) and (6),<·>represents an averaging process; r represents the responsivity of the detector 21, P₀Indicating the power, RP, of the laser light output by the laser 12₀The multiplicative component is represented.

In at least one embodiment, the original frequency jittered signal synchronization detection module 24 outputs coef (f)_d) The two-times frequency jitter signal synchronous detection module 22 outputs coef (2 f)_d) Wherein coef (f)_d) Representing the amplitude, coef (2 f), of the signal component of the electrical signal generated by the detector 21 having the same frequency as the original frequency dither signal_d) Represents the amplitude of the signal component of the electrical signal generated by detector 21 that has the same frequency as the double frequency dither signal; further, according to the formula (5), it is possible toTo obtain<P_PD·cos(ω_d)>＝coef(f_d) According to the formula (6), a<P_PD·cos(2ω_d)>＝coef(2f_d)。

Since the formula (5) contains

The term, formula (6) contains

Terms, using the basic relation of trigonometric functions

And establishing a unitary quartic equation according to the formula (5) and the formula (6), wherein the unitary quartic equation can be written as the formula (7):

according to the above<P_PD·cos(ω_d)>＝coef(f_d) And<P_PD·cos(2ω_d)>＝coef(2f_d) The above formula (7) can be written as the following formula (7 a):

in formula (7a), P₀Optical phase-shifted cosine mean value caused by R and I drive signals

May be a known value determined in advance, coef (2 f)_d) And coef (f)_d) The values output by the double frequency wobble signal synchronization detection module 22 and the original frequency wobble signal synchronization detection module 24, respectively, are based on equation (7a) and can be based on coef (2 f)_d) And coef (f)_d) To calculate

In at least one embodiment, the signal processor 23 synchronizes coef (f) output from the detection module 24 according to the original frequency jitter signal_d) And coef (2 f) output by the double-frequency dithering signal synchronous detection module 22_d) By solving equation (7a), the result can be obtained

I.e. the modulation depth of the wobble signal.

In at least one embodiment, the phase offset caused by the I-modulator DC Bias offset during the operation of the Auto Bias Controller (ABC)

Is small and therefore, can be considered as

And is

Therefore, normalizing equation (6) can result in the following equation (8):

the following formula (9) can be obtained by performing the square root opening processing on formula (8):

in formula (9), coef (2 f)_d) Output by the double frequency dithering signal synchronous detection module 22; RP₀Represents a multiplicative component, which may be a known quantity;

representing a signal component, i.e. the mean of the values of the optical phase-shifted cosine caused by the I-way drive signal, which may be alreadyAnd (4) knowing the quantity. Therefore, the signal processor 23 can synchronize coef (2 f) output from the detection module 22 with the double frequency dither signal according to equation (9)_d) In combination with known RP₀And

calculating the modulation depth of the jitter signal

In at least one embodiment, the signal processor 23 may also be based on the calculated modulation depth

The current amplitude alpha of the dither signal and the initial modulation depth of the dither signal

A target adjustment amplitude of the dither signal is calculated. Wherein the current amplitude a of the dither signal may be determined by a generation unit of the dither signal, an initial modulation depth of the dither signal

May be predetermined and stored and the generating unit of the dither signal may be, for example, the signal processor 23.

The method for the signal processor 23 to calculate the target adjustment amplitude of the dither signal may be, for example: determining the calculated modulation depth

And initial modulation depth

Whether the target adjustment amplitude is equal or not, if not, calculating the target adjustment amplitude as

Furthermore, if the calculated modulation depth is not zero

And initial modulation depth

And if the target adjustment amplitude is equal to the current amplitude alpha, the target adjustment amplitude is equal to the current amplitude alpha.

In at least one embodiment, as shown in fig. 1, the signal processor 23 may generate a dither signal according to the calculated target adjustment amplitude, superimpose the dither signal on a dc bias voltage, and apply the dc bias voltage on which the dither signal is superimposed to the optical modulator 11, the optical modulator 11 being, for example, a differential IQ mach-zehnder (M-Z) modulator.

The dither signal generated by the signal processor 23 may be represented as α cos (2 π f)_dt). At the beginning, α ═ α₀I.e. alpha₀Is an initial value of the amplitude of the dither signal, alpha₀Can be preset; the signal processor 23, after calculating the target adjustment amplitude, is assigned to α to update the current amplitude of the dither signal.

In at least one embodiment, as shown in FIG. 1, the signal processor 23 may also generate the original frequency dithering signal cos (2 π f)_dt) and a frequency-doubled dither signal cos (4 pi f)_dt), cos (2 π f) generated by the signal processor 23_dt) and cos (4 π f)_dt) can be inputted to the original frequency jittered signal synchronization detection module 24 and the frequency doubled jittered signal synchronization detection module 22, respectively, for detecting coef (f)_d) And coef (2 f)_d)。

In addition, embodiments of the present application may not be limited thereto, for example, the original frequency dither signal cos (2 π f)_dt) and a frequency-doubled dither signal cos (4 pi f)_dt) and a dither signal α cos (2 π f)_dt) may not be generated by the signal processor 23 but by other signal generating units.

In the formulae (7) and (9),

can be presetCalculated and stored, whereby the signal processor 23 can calculate the modulation depth based on the equation (7) or the equation (9)

RP₀Can be used as the multiplicative component in the formula (7) and the formula (9),

can be used as the signal component in the equations (7) and (9).

FIG. 4 is a diagram of computing a multiplicative component RP₀A schematic diagram of the process of (1). As shown in fig. 4, a multiplicative component RP is calculated₀The method comprises the following steps:

operation 401 operates an in-phase modulation unit (IMZM) in mach-zehnder (M-Z) modulator 11 at a quadrature point, a quadrature modulation unit (QMZM) at an extinction point, and signals output by the in-phase modulation unit and the quadrature modulation unit are in-phase or in-phase, e.g., by adjusting V_{DC_I}And V_{DC_Q}To operate the in-phase modulation unit (IMZM) at the quadrature point and the quadrature modulation unit (QMZM) at the extinction point;

operation 402 loads a first dither signal having an amplitude greater than a first amplitude threshold, e.g., the first dither signal may be superimposed on V_{DC_I}And V_{DC_Q}Thus, the mach-zehnder (M-Z) modulator 11 can be loaded with a first dither signal having a frequency of, for example, f_d；

Operation 403, cause both the in-phase modulation unit (IMZM) and the quadrature modulation unit (QMZM) to transmit all-zero signals;

operation 404 calculates a first amplitude Coef (f) of a signal component having the same frequency as the first dither signal included in an electrical signal obtained by detecting an optical signal output from a mach-zehnder (M-Z) modulator_d) And a second amplitude Coef (3 f) of the signal component having a frequency 3 times the frequency of the first dither signal_d) For example, the optical signal output from the Mach-Zehnder (M-Z) modulator 11 is detected by the detector 21 at a frequency f_dThe dither signal of (2) synchronizes the electrical signal output by the detector 21Detecting to obtain a first amplitude Coef (f)_d) Using a frequency of 3f_dThe electrical signal output by the detector 21 is synchronously detected by the jitter signal to obtain a second amplitude Coef (3 f)_d) The specific method of synchronous detection can refer to the above formulas (4) and (5); in addition, first amplitude Coef (f)_d) The second amplitude Coef (3 f) can be calculated by the original frequency jitter signal synchronization detection module 24_d) May be calculated by a triple frequency jitter signal synchronization detection module, wherein the triple frequency jitter signal synchronization detection module may be a component of the apparatus 2 for monitoring the modulation depth of the jitter signal, or may be provided independently of the apparatus 2 for monitoring the modulation depth of the jitter signal, and the obtained first amplitude Coef (f) in operation 404_d) And a second amplitude Coef (3 f)_d) Can be expressed as:

operation 405, according to a first magnitude Coef (f)_d) And a second amplitude Coef (3 f)_d) Calculating a multiplicative component RP₀For example, the multiplicative component is calculated using the following equation:

further, the multiplicative component RP calculated in operation 405₀May be stored in the signal processor 23.

FIG. 5 is a diagram of calculating signal components

A schematic diagram of the process of (1). As shown in fig. 5, the method of calculating a signal component includes:

operation 501 of bringing Mach-Zehnder (M-Z) modulators 11 into phaseThe modulation unit (IMZM) operates at a quadrature point, the quadrature modulation unit (QMZM) operates at an extinction point, and the signals output by the in-phase modulation unit and the quadrature modulation unit are brought into or out of phase, e.g. by adjusting V_{DC_I}And V_{DC_Q}To operate the in-phase modulation unit (IMZM) at the quadrature point and the quadrature modulation unit (QMZM) at the extinction point;

operation 502, causing an in-phase modulation unit (IMZM) to transmit a transmission signal and a quadrature modulation unit (QMZM) to transmit an all-zero signal;

operation 503 loads a second wobble signal having an amplitude greater than a second amplitude threshold, or less than a third amplitude threshold, the second amplitude threshold being greater than the third amplitude threshold, the second wobble signal having a frequency f, for example_d；

Operation 504 calculates a third amplitude Coef (f) of a signal component having the same frequency as the second dither signal included in an electrical signal obtained by detecting the optical signal output from the mach-zehnder (M-Z) modulator 11_d) For example, the optical signal output from the Mach-Zehnder (M-Z) modulator 11 is detected by the detector 21 at a frequency f_dThe electrical signal output by the detector 21 is synchronously detected by the jitter signal to obtain a third amplitude Coef (f)_d) Third amplitude Coef (f)_d) Can be expressed as

Operation 505, causing both the in-phase modulation unit (IMZM) and the quadrature modulation unit (QMZM) to transmit all-zero signals;

operation 506 of calculating a fourth amplitude of a signal component having the same frequency as the second dither signal included in an electrical signal obtained by detecting the optical signal output from the mach-zehnder (M-Z) modulator 11

A fourth amplitude

Can be expressed as

Operation 507, according to the third amplitude coef (fd) and the fourth amplitude

Calculating signal components

For example, the signal component is calculated using the following equation:

further, the signal component calculated in operation 507 may be stored in the signal processor 23.

FIG. 6 is a diagram of setting the initial modulation depth

A schematic diagram of the process of (1). As shown in fig. 6, the method of setting the initial modulation depth may include:

operation 601 determines a first allowable range of modulation depth according to the bit error cost requirement, for example, the first allowable range is

In operation 601, for example, the mach-zehnder (M-Z) modulator 11 may not be loaded with the dither signal, and the error rate may be calculated without the dither signal, and then loaded with the frequency f_dAnd cosine jitter signals with the amplitude of alpha, changing the value of the amplitude alpha of the jitter signals, calculating error code cost caused by different amplitudes of the jitter signals, and further determining the first allowable range;

operation 602 determines a second allowable range of modulation depth based on sensitivity requirements, such as

In operation 602, mach-zehnder modulator (mach-zehnder modulator)M-Z) modulator 11 is loaded with a frequency f_dAnd the cosine jitter signal with the amplitude of alpha, changing the value of the amplitude alpha of the jitter signal, calculating the sensitivity corresponding to different amplitudes of the jitter signal, and further determining the second allowable range;

operation 603 determines a range of modulation depths according to the first allowable range and the second allowable range, for example, with the smaller of the upper values of the first allowable range and the second allowable range as the upper value of the range of modulation depths, with the larger of the lower values of the first allowable range and the second allowable range as the lower value of the range of modulation depths, that is,

and

operation 604 determines an initial modulation depth from a range of modulation depths

For example, a value is arbitrarily selected from the range of modulation depths determined in operation 603 as the initial modulation depth

Further, the initial modulation depth obtained in operation 604

May be stored in the signal processor 23.

Second aspect of the embodiments

A second aspect of the embodiments of the present application provides a method for monitoring a modulation depth of a dither signal, which corresponds to the apparatus for monitoring a modulation depth of a dither signal of the first aspect of the embodiments of the present application.

Fig. 7 is a schematic diagram of a method for monitoring a modulation depth of a jittered signal according to a second aspect of an embodiment of the present application. As shown in fig. 7, the method of monitoring the modulation depth of the dither signal includes:

operation 701, detecting an optical signal output from a mach-zehnder (M-Z) modulator to obtain an electrical signal, wherein a dc bias voltage applied to the mach-zehnder modulator is superimposed with a predetermined frequency (f)_d) The dither signal of (2);

operation 702, couple the electrical signal with a frequency 2 times (2 f) the predetermined frequency_d) The two times frequency jitter signal is synchronously detected to obtain the amplitude Coef (2 f) of the signal component which is contained in the electric signal and has the same frequency as the two times frequency jitter signal_d) (ii) a And

operation 703, according to the amplitude Coef (2 f) of the signal component having the same frequency as the double frequency dither signal_d) Calculating the modulation depth of the dither signal superimposed on the DC bias voltage

In at least one embodiment, in operation 703, a power P of laser light output by a laser providing an optical carrier for a Mach-Zehnder modulator may be based on a responsivity R of a detector for detecting an optical signal₀Of a signal component

And an amplitude Coef (2 f) of a signal component having the same frequency as the frequency of the double frequency dither signal_d) Calculating modulation depth

For example, the modulation depth is calculated using the above formula (9)

As shown in fig. 7, the method of monitoring the modulation depth of the dither signal may further include:

operation 704, the electrical signal is summed to a predetermined frequency (f)_d) The original frequency jitter signal is synchronously detected to obtain the amplitude Coef (f) of the signal component which is contained in the electric signal and has the same frequency as the original frequency jitter signal_d)。

With operation 704, in operation 703, the amplitude Coef (2 f) of the signal component having the same frequency as the double frequency dither signal may be based on_d) And the amplitude Coef (f) of the signal component with the same frequency as the original frequency jitter signal_d) Calculating the modulation depth of the dither signal

In at least one embodiment, with operation 704, in operation 703, a power P of laser light output by a laser providing an optical carrier for a mach-zehnder modulator may be based on a responsivity R of a detector for detecting an optical signal₀Of a signal component

Coef(2f_d) And Coef (f)_d) Calculating modulation depth

For example, the modulation depth is calculated using the above formula (7)

operation 705. based on the calculated modulation depth

And the current amplitude and the initial modulation depth of the dither signal, calculating the purpose of the dither signalAnd (5) calibrating the amplitude.

As shown in fig. 7, operation 705 may include:

operation 7051, judge the calculated modulation depth

And initial modulation depth

Whether equal, if not equal, proceed to operation 7052, if equal, proceed to operation 7053;

operation 7052, set target adjustment amplitude to

Operation 7053 sets the target adjustment amplitude equal to the current amplitude.

Further, in at least one embodiment, as shown in fig. 7, the method may further comprise:

operation 706 generates a dither signal according to the target adjustment amplitude of the dither signal, superimposes the generated dither signal on a dc bias voltage, and applies the dc bias voltage to the mach-zehnder (M-Z) modulator.

In at least one embodiment, as shown in fig. 7, the method of monitoring the modulation depth of the dither signal may further include:

operation 707, calculate multiplicative component RP₀Of a signal component

And initial modulation depth

In operation 707, a multiplicative component RP is calculated₀May be calculated as shown in fig. 4, calculating the signal component

The method (2) is shown in FIG. 5Calculating an initial modulation depth

The method of (3) can be as shown in fig. 6.

In the second aspect of the embodiments of the present application, regarding the description of each step in the method for monitoring the modulation depth of the dither signal, reference may be made to the detailed description of each unit in the apparatus for monitoring the modulation depth of the dither signal of the first aspect of the embodiments of the present application.

According to the second aspect of the embodiments of the present application, the optical signal output by the mach-zehnder (M-Z) modulator is detected to obtain the electrical signal, and the modulation depth of the dither signal is calculated according to the amplitude of the dither signal with twice frequency included in the electrical signal, so that the modulation depth of the dither signal can be accurately monitored, the amplitude of the dither signal can be reasonably adjusted, and the modulation depth can be controlled within a reasonable range.

Third aspect of the embodiments

A third aspect of embodiments of the present application provides an optical transmitter, including: the apparatus for monitoring the modulation depth of a jittered signal according to the first aspect of the embodiment.

Fig. 8 is a schematic block diagram of a system configuration of an optical transmitter of the third aspect of the embodiment of the present application. As shown in fig. 8, the optical transmitter 800 includes: a signal generator 801, a processing unit 802, a digital-to-analog converter 803, a modulator 804, a photodiode 805, and a control unit 806, wherein:

the signal generator 801 generates two paths of digital signals according to the transmission data, and the two paths of digital signals are used as driving signals of an I path and a Q path of the modulator 804; the processing unit 802 performs mutual interference processing on the driving signals of the I path and the Q path of the modulator 804; the digital-to-analog conversion unit 803 performs digital-to-analog conversion on the drive signals of the I path and the Q path after the mutual interference processing; the modulator 804 modulates light according to the driving signal; photodiode 805 detects the output power signal of modulator 804; the control unit 806 controls the dc bias voltage of the modulator 804 according to the output power signal.

In this embodiment, the structures of the signal generator 801, the digital-to-analog converter 803, the modulator 804 and the photodiode 805 can refer to the prior art, and the structure and function of the control unit 806 are the same as those of the apparatus for monitoring the modulation depth of the dither signal in the first aspect of the embodiment, and are not described herein again.

In addition, the control unit 806 may be integrated in a digital signal processor of the optical transmitter, i.e. the function of the control unit 806 is realized by the digital signal processor.

In this embodiment, the optical transmitter 800 also does not necessarily include all of the components shown in FIG. 8; the optical transmitter 800 may also include components not shown in fig. 8, as may be found in the prior art.

Embodiments of the present application also provide a computer-readable program, wherein when the program is executed in an apparatus or an optical transmitter for monitoring a modulation depth of a dither signal, the program causes the apparatus or the optical transmitter for monitoring a modulation depth of a dither signal to execute the method for monitoring a modulation depth of a dither signal according to the second aspect of the embodiments.

The present embodiment also provides a storage medium storing a computer readable program, where the storage medium stores the above computer readable program, and the computer readable program enables an apparatus or an optical transmitter for monitoring a modulation depth of a dither signal to execute the method for monitoring a modulation depth of a dither signal according to the second aspect of the present embodiment.

The means described in connection with the embodiments of the invention may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. For example, one or more of the functional block diagrams and/or one or more combinations of the functional block diagrams illustrated in the figures may correspond to individual software modules, or may correspond to individual hardware modules of a computer program flow. These software modules may correspond to respective operations in the method. These hardware modules may be implemented, for example, by solidifying these software modules using a Field Programmable Gate Array (FPGA).

A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. A storage medium may be coupled to the processor such that the processor can read information from, and write information to, the storage medium; or the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The software module may be stored in the memory of the mobile terminal or in a memory card that is insertable into the mobile terminal. For example, if the electronic device employs a MEGA-SIM card with a larger capacity or a flash memory device with a larger capacity, the software module may be stored in the MEGA-SIM card or the flash memory device with a larger capacity.

One or more of the functional block diagrams and/or one or more combinations of the functional block diagrams described with respect to the figures may be implemented as a general purpose processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any suitable combination thereof designed to perform the functions described herein. One or more of the functional block diagrams and/or one or more combinations of the functional block diagrams described with respect to the figures may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP communication, or any other such configuration.

The present application has been described in conjunction with specific embodiments, but it should be understood by those skilled in the art that these descriptions are intended to be illustrative, and not limiting. Various modifications and adaptations of the present application may occur to those skilled in the art based on the teachings herein and are within the scope of the present application.

With respect to the embodiments including the above embodiments, the following remarks are also disclosed:

1. an apparatus for monitoring a modulation depth of a dither signal, comprising:

a detector which detects an optical signal output from the mach-zehnder modulator to obtain an electrical signal, wherein a dither signal of a predetermined frequency is superimposed on a dc bias voltage applied to the mach-zehnder modulator;

a double-frequency dither signal synchronous detection module, configured to perform synchronous detection on the electrical signal output by the detector and a double-frequency dither signal with a frequency 2 times that of the predetermined frequency to obtain an amplitude of a signal component included in the electrical signal output by the detector and having a frequency identical to that of the double-frequency dither signal; and

and the signal processor calculates the modulation depth of the dither signal superposed on the DC bias voltage according to the amplitude of the double-frequency dither signal.

2. The apparatus according to supplementary note 1, wherein,

and the signal processor calculates the modulation depth according to the responsivity of the detector, the power of the laser output by the laser for providing the optical carrier for the Mach-Zehnder modulator, the signal component and the amplitude of the signal component with the same frequency as the frequency of the double-frequency jitter signal.

3. The apparatus recited in supplementary note 2, wherein the signal processor calculates the modulation depth according to equation (9) below:

wherein R is the responsivity of the detector, P₀Is the power of the laser;

is the signal component; coef (2 f)_d) Is the amplitude of the signal component at the same frequency as the double frequency dither signal.

4. The apparatus according to supplementary note 1, wherein the apparatus further comprises:

an original frequency jitter signal synchronous detection module, which is used for synchronously detecting the electric signal output by the detector and an original frequency jitter signal with the frequency being the preset frequency to obtain the amplitude of a signal component which is contained in the electric signal output by the detector and has the same frequency as the original frequency jitter signal,

and the signal processor calculates the modulation depth of the dither signal superposed on the DC bias voltage according to the amplitude of the double-frequency dither signal and the amplitude of the original frequency dither signal.

5. The apparatus according to supplementary note 4, wherein,

and the signal processor calculates the modulation depth according to the responsivity of the detector, the power of the laser output by the laser for providing optical carrier waves for the Mach-Zehnder modulator, the signal component, the amplitude of the signal component with the same frequency as the double-frequency jitter signal and the amplitude of the signal component with the same frequency as the original frequency jitter signal.

6. The apparatus as set forth in supplementary note 5, wherein,

the signal processor calculates the modulation depth by solving the following equation (7 a):

wherein R is the responsivity of the detector, P₀Is the power of the laser light and,

is the signal component, ω_dIs the circular frequency corresponding to the frequency of the wobble signal.

7. The apparatus according to supplementary note 1, wherein,

and the signal processor also calculates the target adjustment amplitude of the jitter signal according to the calculated modulation depth, the current amplitude of the jitter signal and the initial modulation depth.

8. A method of monitoring the modulation depth of a dither signal, comprising:

detecting an optical signal output by a Mach-Zehnder modulator to obtain an electrical signal, wherein a direct current bias voltage applied to the Mach-Zehnder modulator is superposed with a jitter signal with a preset frequency;

synchronously detecting the electric signal and a frequency-doubled jittering signal with the frequency 2 times of the preset frequency to obtain the amplitude of a signal component contained in the electric signal and having the same frequency as the frequency of the frequency-doubled jittering signal; and

according to the amplitude (Coef (2 f) of the frequency-doubled dither signal_d) Calculating a modulation depth of the dither signal superimposed on the dc bias voltage.

9. The method according to supplementary note 8, wherein calculating the modulation depth according to the amplitude of the frequency-doubled dither signal comprises:

and calculating the modulation depth according to the responsivity of a detector for detecting the optical signal, the power of laser light output by a laser for providing the Mach-Zehnder modulator with optical carrier, the signal component and the amplitude of the signal component with the same frequency as the frequency of the double-frequency jitter signal.

10. The method according to supplementary note 9, wherein the modulation depth is calculated according to the following equation (9):

wherein R is the responsivity of the detector, P₀Is the power of the laser;

11. The method according to supplementary note 8, wherein the method further comprises:

synchronously detecting the electric signal and an original frequency jitter signal with the frequency of the preset frequency to obtain the amplitude of a signal component contained in the electric signal and having the same frequency as the original frequency jitter signal,

and calculating the modulation depth of the dither signal superposed on the direct-current bias voltage according to the amplitude of the signal component with the same frequency as the frequency of the dither signal with the double frequency and the amplitude of the signal component with the same frequency as the original frequency of the dither signal.

12. The method according to supplementary note 11, wherein calculating the modulation depth of the dither signal superimposed on the dc offset voltage according to the amplitude of the frequency-doubled dither signal and the amplitude of the original frequency dither signal includes:

and calculating the modulation depth according to the responsivity of a detector for detecting the optical signal, the power of the laser output by the laser for providing the optical carrier for the Mach-Zehnder modulator, the signal component, the amplitude of the signal component with the same frequency as the frequency of the double-frequency jitter signal and the amplitude of the signal component with the same frequency as the original frequency jitter signal.

13. The method according to supplementary note 12, wherein the modulation depth is calculated by solving the following equation (7 a):

14. The method according to supplementary note 8, wherein the method further comprises:

and calculating the target adjustment amplitude of the jitter signal according to the calculated modulation depth, the current amplitude of the jitter signal and the initial modulation depth.

15. The method according to supplementary note 8, wherein the method further comprises:

making an in-phase modulation unit work at a quadrature point and a quadrature modulation unit work at an extinction point in the Mach-Zehnder modulator, and making signals output by the in-phase modulation unit and the quadrature modulation unit in the same phase or in opposite phase;

loading a first dither signal, an amplitude of the first dither signal being greater than a first amplitude threshold;

causing both the in-phase modulation unit and the quadrature modulation unit to transmit all-zero signals;

calculating a first amplitude of a signal component with the same frequency as the first jitter signal and a second amplitude of a signal component with the frequency 3 times that of the first jitter signal, which are contained in an electric signal obtained by detecting the optical signal output by the Mach-Zehnder modulator;

and calculating a multiplicative component according to the first amplitude and the second amplitude, wherein the multiplicative component is used for calculating the modulation depth.

16. The method of supplementary note 15, wherein the method further comprises:

enabling the in-phase modulation unit to send a transmission signal, and enabling the quadrature modulation unit to send an all-zero signal;

loading a second dither signal, wherein the amplitude of the second dither signal is greater than a second amplitude threshold or less than a third amplitude threshold, and the second amplitude threshold is greater than the third amplitude threshold;

calculating a third amplitude of a signal component which is contained in an electric signal obtained by detecting the optical signal output by the Mach-Zehnder modulator and has the same frequency as the second jitter signal;

calculating a fourth amplitude of a signal component which is contained in an electric signal obtained by detecting the optical signal output by the Mach-Zehnder modulator and has the same frequency as the second jitter signal; and

and calculating a signal component according to the third amplitude and the fourth amplitude, wherein the signal component is used for calculating the modulation depth.

17. The method of supplementary note 16, wherein the method further comprises:

determining a first allowable range of modulation depth according to the requirement of error code cost;

determining a second allowable range of modulation depth according to the sensitivity requirement;

determining a range of modulation depths according to the first allowable range and the second allowable range; and

an initial modulation depth is determined from the range of modulation depths.

Claims

1. An apparatus for monitoring a modulation depth of a dither signal, said apparatus comprising:

2. The apparatus of claim 1, wherein,

3. The apparatus of claim 2, wherein the signal processor calculates the modulation depth according to equation (9) as follows:

wherein R is the responsivity of the detector, P₀Is the power of the laser;

4. The apparatus of claim 1, wherein the apparatus further comprises:

5. The apparatus of claim 4, wherein,

6. The apparatus of claim 5, wherein the signal processor calculates the modulation depth by solving the following equation (7 a):

7. The apparatus of claim 1, wherein,

8. An optical transmitter having an apparatus for monitoring the modulation depth of a dither signal according to any one of claims 1 to 7.

9. A method of monitoring a modulation depth of a jittered signal, the method comprising:

and calculating the modulation depth of the dither signal superposed on the DC bias voltage according to the amplitude of the frequency-doubled dither signal.

10. The method of claim 9, wherein the method further comprises: